SPECIATION OF TRIHALOMETHANE MIXTURES FOR THE MISSISSIPPI-RIVER, MISSOURI-RIVER, AND OHIO-RIVER

Trihalomethane formation potentials were determined for the chlorinati on of water samples from the Mississippi, Missouri, and Ohio Rivers. S amples were collected during the summer and fall of 1991 and the sprin g of 1992 at 12 locations on the Mississippi from New Orleans, LA, to Minneapolis, MN, and on the Missouri and Ohio 1.6 km upstream from the ir confluences with the Mississippi. Formation potentials were determi ned as a function of pH and initial free-chlorine concentration. Chlor oform concentrations decreased with distance downstream and approximat ely paralleled the decrease of the dissolved organic-carbon concentrat ion. Bromide concentrations were 3.7-5.7 times higher for the Missouri and 1.4-1.6 times higher for the Ohio than for the Mississippi above their confluences, resulting in an overall increase of the bromide con centration with distance downstream. Variations of the concentrations of the brominated trihalomethanes with distance downstream approximate ly paralleled the variation of the bromide concentration. Concentratio ns of all four trihalomethanes increased as the pH increased. Concentr ations of chloroform and bromodichloromethane increased slightly and t he concentration of bromoform decreased as the initial free-chlorine c oncentration increased; the chlorodibromomethane concentration had lit tle dependence on the free-chlorine concentration.